The conformations of the DNAs and RNAs have been of great interest because an understanding of how they work follows from a knowledge of their forms. We are determining the detailed molecular conformations of entire nucleic acid molecules, using classical potential energy calculations, and minimizing the energy as a function of all conformational angles simultaneously. This approach was successfully employed by Stellman et al. to predict both the correct conformation and the packaging scheme in the crystal of Ca plus 2 GpC. Calculations by Broyde, et al. for other RNA subunit molecules are also in good agreement with experimental data. We propose to extend these types of calculations to dimeric subunits of DNA, in order to establish the effect of the bases on their conformations, and to elucidate more fully the conformational differences between the DNAs and RNAs, and between the A and B forms of the DNAs. It is also proposed to calculate conformations for dimeric subunits of RNA which contain rare nucleotides occurring in the loops of tRNAs, in order to examine the role that these less common species play. Further calculations are to be made for various base sequences of trimeric RNA and DNA subunits, to establish whether the conformations of these larger units are more restricted than for dimers. Finally, conformational calculations are to be made for double stranded subunits, as a basis for future calculations of the interaction of drugs with DNA.